The color of your rock suggests that your tank may be relatively new?
IIRC, Fromia stars like Patrick get most of their food from biofilm, and really want a mature tank with lots of organisms growing on every square centimeter of rock. He may be having a hard time finding enough to eat.
You can try placing some nutrition alongside him, and see if he goes for it, but . . .
How long have you had it? It’s also pretty normal for them to just fall apart within a month of getting them due to rough handling during transport, acclimation, etc.